Promoted antimony-iron oxidation catalyst



United States Patent US. Cl. 252--456 4 Claims ABSTRACT OF THEDISCLOSURE Catalysts are provided which are useful in the oxidation ofolefins to aldehydes and conjugated dienes and in the ammoxidation ofolefins to nitriles, and which are composed of antimony oxide, ironoxide and oxides of certain promoter elements on a silica carrier.

This is a continuation-in-part application based on our copending US.patent application Ser. No. 507,715 filed Nov. 15, 1965, now abandoned,which in turn is a continuation-in-part application based on US. patentapplication Ser. No. 311,630 filed Sept. 26, 1963, and now abandoned.

This invention relates to promoted oxidation catalysts comprising oxidesof antimony and iron with a small amount of a metal or metal oxidepromoter which are useful for the catalytic oxidation of olefins toaldehydes and conjugated dienes and for the catalytic ammoxidation ofolefins to nitriles. The catalytic oxidation reactions are exemplifiedby the oxidation of propylene to acrolein, the oxidation of isobutyleneto methacrolein, the oxydehydrogenation of an olefin having 4 to 8carbons, such as the oxydehydrogenation of butene-1 to butadiene-1,3,the ammoxidation of propylene to acrylonitrile and the ammoxidation ofisobutylene to methacrylonitrile.

The promoted antimony oxide-iron oxide catalysts are based on theantimony oxide-iron oxide catalysts disclosed in US. Pat. No. 3,197,419.Attrition resistant catalysts of these types are described morecompletely in US. Pat. No. 3,341,471

The antimony oxide-iron oxide base catalyst disclosed in theaforementioned patents is referred to as a mixture of antimony and ironoxides, but this is not to be construed as meaning that the catalyst iscomposed either in Whole or in part of these compounds. The proportionsof antimony and iron in the catalyst system vary widely. The Sb:Featomic ratio can range from about 1:50 to about 99:1. However, optimumactivity appears to be obtained at Sb:Fe atomic ratios within the rangeof from 1:1 to 25: 1.

The catalyst of this invention contains from to 95% by weight of asilica support and preferably at least 10% up to about 90% of thesupporting silica by weight of the entire composition is employed.

In the preparation of the base catalyst useful in this invention, theantimony oxide and iron oxide can be blended together, or can be formedseparately and then blended or formed separately or together in situ.

The iron oxide component of the base catalyst useful herein can beprovided in the form of ferrous, ferric or ferrous-ferric oxides, or byprecipitation in situ from a soluble ion salt, such as the nitrate,acetate, or a halide, such as the chloride. Free iron can be used as astarting material, and if antimony metal is also employed, the antimonycan be converted to the oxide and the iron to p we the nitratesimultaneously by oxidation in hot nitric acid. A slurry of hydrousantimony oxide in nitric acid can be combined with a solution of an ironsalt, such as ferric nitrate, which is then precipitated in situ asferric hydroxide by making the solution alkaline with ammoniumhydroxide, the ammonium nitrate and the other ammonium salts beingremoved by filtration of the resulting slurry or by thermaldecomposition.

It will be apparent from the above that ferrous and ferric bromides,chlorides, fluorides and iodides, nitrates, acetates, sulfites,sulfates, phosphates, thiocyanates, thiosulfates, oxalates, formates andhydroxides can be employed as the source of the iron oxide component.

The catalytic activity of the novel promoted catalysts embodied in thepresent invention, is enhanced by heating the catalyst at an elevatedtemperature. Preferably, the catalyst mixture is dried and heated at atemperature of from 500 to 1500 F., more preferably at about 700 to 900F., for from two to twenty-four hours. If activity then is notsufiicient, the catalyst can be further heated at a temperature aboveabout 1000 F. but below a temperature deleterious to the catalyst atwhich it is melted or decomposed, preferably from about 1400 F. to about1900 F. for from one to forty-eight hours, in the presence of oxygen oran oxygen-containing gas, such as air. Usually this limit is not reachedbefore 2000 F. and in some cases, this temperature can be exceeded.

In general, the higher the activation temperature, the less timerequired to effect activation. The sufliciency of activation at anygiven set of conditions is ascertained by a spot test of a sample of thematerial for catalytic activity. Activation is best carried out in anopen chamber, permitting circulation of air or oxygen, so that anyoxygen consumed will be replaced.

The antimony oxide-iron oxide base catalyst composition useful in thepresent invention can be defined by the following empirical formula:

Sb Fe O Where a is 1 to 99, b is 50 to 1, and c is a number taken tosatisfy the average valences of antimony and iron in the oxidationstates in which they exist in the catalyst as defined by the empiricalformula above. Thus, the Sb valence may range from 3 to 5 and the Fevalence from 2 to 3.

Metals selected from Groups I-B, II-A, II-B, IIIA, IVA, IV-B, V-A, V-B,VI-A, VI-B, VII-B and VIII of the Periodic Table have been found toenhance the activity of the above-described antimony-iron oxide catalystfor the conversion of olefins to aldehydes, diolefins and nitriles.Specific metals which function as promoters in combination with the basecatalysts are bismuth, copper, tin, germanium, rhenium, niobium, silver,tellurium, tungsten, gallium, lead, tantalum, palladium, cadmium,Zirconium, vanadium, nickel, titanium, cobalt, molybdenum, zinc, barium,calcium, thallium, arsenic and rhodium. Most preferred promoter metalsare bismuth, copper, tin, germanium, rhenium, niobium, silver,tellurium, tungsten, gallium, lead, tantalum, palladium, cadmium,zirconium, molybdenum, zinc, barium, calcium, thallium and arsenic.These promoter metals are incorporated into the base catalyst preferablyin the form of their oxides in amounts from about 0.01 to 20% by weightbased on the weight of. the promoted base antimony-iron oxide catalystexclusively of the carrier material. Most preferred is a range of fromabout 1 to 10% by weight of the promoter element based on the baseantimony oxide-iron oxide catalyst.

The promoter elements may be incorporated into the base catalyst byco-precipitation, by impregnation, or by other means.

3 OXIDATION OF OLEFINS TO OXYGENATED COMPOUNDS The reactants used in theoxidation to oxygenated compounds are oxygen and an olefin having onlythree carbon atoms in a straight chain such as propylene or isobutyleneor mixtures thereof.

The olefins may be in admixture with paratfinic hydrocarbons, such asethane, propane, butane and pentane; for example, a propylene-propanemixture may constitute the feed. This makes it possible to use ordinaryrefinery streams without special preparation.

The temperature at which this oxidation is conducted may varyconsiderably depending upon the catalyst, the particular olefin beingoxidized and the correlated conditions of the rate of throughput orcontact time and the ratio of olefin to oxygen. In general, whenoperating at pressures near atmospheric, i.e., to 100 p.s.i.g.,temperatures in the range of 500 to 1100 F. may be advantageouslyemployed. However, the process may be conducted at other pressures, andin the case where superatmospheric pressures, e.g., above 100 p.s.i.g.,are employed, somewhat lower temperatures are possible. In the casewhere this process is employed to convert propylene to acrolein, atemperature range of 750 to 950 F. has been found to be optimum atatmospheric pressure.

While pressures other than atmospheric may be employed, it is generallypreferred to operate at or near atmospheric pressure, since the reactionproceeds well at such pressures and the use of expensive high pressureequipment is avoided.

The apparent contact time employed in the process is not critical and itmay be selected from a broad operable range which may vary from 0.1 to50 seconds. The apparent contact time may be defined as the length oftime in seconds which the unit volume of gas measured under theconditions of reaction is in contact with the apparent unit volume ofthe catalyst. It may be calculated, for example, from the apparentvolume of the catalyst bed, the average temperature and pressure of thereactor, and the fiow rates of the several components of the. reactionmixture.

The optimum contact time will, of course, vary depending upon the olefinbeing treated, but in the case of propylene and isobutylene, thepreferred apparent contact time is 0.15 to seconds.

A molar ratio of oxygen to olefin between about 0.5:1 to 5:1 generallygives the most satisfactory results. For the conversion of propylene toacrolein, a preferred ratio of oxygen to olefin is from about 1:1 toabout 2:1. The oxygen used in the process may be derived from anysource; however, air is the least expensive source of oxygen and ispreferred for that reason.

We have also discovered that the addition of water to the reactionmixture has a marked beneficial influence on the course of the reactionin that it improves the conversion and the yields of the desiredproduct. The manner in which water affects the reaction is not fullyunderstood but the theory of this phenomenon is not deemed important inview of the experimental results we have obtained. Accordingly, weprefer to include water in the re.- action mixture. Generally, a ratioof olefin to water in the reaction mixture of from 120.5 to 1:10 willgive very satisfactory results, and a ratio of from 1:0.75 to 1:6 hasbeen found to be optimum when converting propylene to acrolein, Thewater, of course, will be in the vapor phase during the reaction.

Inert diluents, such as nitrogen and carbon dioxide, may be present inthe reaction mixture.

OXIDATION OF OLEFINS TO NITRILES The reactants are the same as thoseused in the oxidation of olefins to aldehydes described above exceptthat ammonia is included as a reactant. Any of the olefins describedabove can be used.

In its preferred aspect, the process comprises contacting a mixturecomprising propylene or isobutylene, ammonia and oxygen with thepromoted catalyst of this invention at an elevated temperature and atatmospheric or near atmospheric pressure.

Any source of oxygen may be employed in this process. For economicreasons, however, it is preferred that air be employed as the source ofoxygen. From a purely technical viewpoint, relatively pure molecularoxygen will give equivalent results. The molar ratio of oxygen to theolefin in the feed to the reaction vessel should be in the range of0.5:1 to 4:1 and a ratio of about 1:1 to 3:1 is preferred.

Low molecular weight saturated hydrocarbons do not appear to influencethe reaction to an appreciable degree, and these materials can bepresent; consequently, the addition of saturated hydrocarbons to thefeed to the reaction is contemplated within the scope of this invention.Likewise, diluents, such as nitrogen and the oxides of carbon, may bepresent in the reaction mixture without deleterious effect.

The molar ratio of ammonia to olefin in the feed to the reactor may varybetween about 0.05:1 to 5 :1. There is no real upper limit for theammonia:olefin ratio, but there is generally no reason to exceed the 5:1ratio. At ammoniazolefin ratios appreciably less than the stoichiometricratio of 1:1, various amounts of oxygenated derivatives of the olefinwill be formed.

Significant amounts of unsaturated aldehydes, as Well as nitriles, willbe obtained at ammonia-olefin ratios substantially below 1: 1, i.e., inthe range of 0.15:1 to 0.75: 1. Outside the upper limit of this rangeonly insignificant amounts of aldehydes will be produced, and only verysmall amounts of nitriles will be produced at ammonia: olefin ratiosbelow the lower limit of this range. It is fortuitous that within theammonia-olefin range stated, maximum utilization of ammonia is obtainedand this is highly desirable. It is generally possible to recycle anyunreacted olefin and unconverted ammonia.

A particularly surprising aspect of this invention is the efiect ofwater on the course of the reaction. We have found that in many caseswater in the mixture fed to the reaction vessel improves the selectivityof the reaction and the yield of nitrile. However, reactions notincluding water in the feed are not to be excluded from this inventioninasmuch as water is formed in the course of the reaction.

In general, the molar ratio of added water to olefin, when water isadded, is at least about 0.25:1. Ratios on the order of 1:1 to 3:1 areparticularly desirable, but higher ratios may be employed, i.e., up toabout 10: 1.

The reaction is carried out at a temperature within the range of fromabout 550 to 1100 F. The preferred temperature range is from about 800to 1000 F.

The pressure at which the reaction is conducted is also an importantvariable, and the reaction should be carried out at about atmospheric orslightly above atmospheric (2 to 3 atmospheres) pressure. In general,high pressures, i.e., about 250 p.s.i.g., are not suitable, since higherpressures tend to favor the formation of undesirable by-products.

The apparent contact time is not critical, and contact times in therange of from 0.1 to about seconds may be employed. The optimum contacttime will, of course, vary depending upon the olefin being treated, butin general, a contact time of from 1 to 15 seconds is preferred.

THE OXIDATIVE DEHYDROGENATION OF OLEFINS TO DIOLEFINS AND AROMATICS Inaccordance with the present invention, this promoted catalyst system isemployed in the catalytic oxidative dehydrogenation of olefins todiolefins and aromatic compounds. In the process, the feed stream invapor form containing the olefin to be dehydrogenated and oxygen isconducted over the promoted catalyst at a comparatively low temperatureto obtain the corresponding diolefin or aromatic compound.

By the term olefin as used herein is meant the open chain as well ascyclic olefins. The olefins dehydrogenated in accordance with thisinvention have at least four and up to about eight nonquaternary carbonatoms, of which at least four are arranged in series in a straight chainor ring. The olefins preferably are either normal straight chain ortertiary olefins. Both cis and trans isomers, where they exist, can bedehydrogenated.

Among the many olefinic compounds which can be dehydrogenated in thisWay are butene-l; butene-2; pentene-1; pentene-2; tertiary pentenes andhexenes having one tertiary carbon atom such as Z-methyLpentene-l, 3-methylbutene 1,3,4 dimethyl pentene 1, 4 methylpentene-2; heptene-l;octene-l; cyclopentene; cyclohexene; B-methyl cyclohexene andcycloheptene.

Open chain olefins yield diolefins, and, in general, sixmembered ringolefins yield aromatic ring compounds. The higher molecular weight openchain olefins may cyclize to aromatic ring compounds.

The feed stock in addition to the olefin and oxygen can contain one ormore parafiinic or naphthenic hydrocarbons having up to about ten carbonatoms, which may be present as impurities in some petroleum hydrocarbonstocks and which may also be dehydrogenated in some cases. In thisoxidative dehydrogenation reaction, propylene and isobutylene should notbe included in the feed in substantial amounts.

The amount of oxygen should be within the range of from about 0.3 toabout 3 moles per mole of olefin. Stoichiometrically, 0.5 to 1.5 molesof oxygen per mole of olefin is required for the dehydrogenation todiolefins and aromatics respectively. It is preferred to employ anexcess of oxygen, from 1 to about 2 moles per mole of olefin, in orderto ensure a higher yield of diolefin per pass. The oxygen can besupplied as pure or substantially pure oxygen or as air or in the formof hydrogen peroxide.

When pure oxygen is used, it may be desirable to incorporated a diluentin the mixture such as steam, carbon dioxide or nitrogen.

The feed stock is preferably catalytically dehydrogenated in thepresence of steam, but this is not essential. Usually, from about 0.1 toabout 6 moles of steam per mole of olefin reactant is employed, butamounts larger than this can be used.

The dehydrogenation proceeds at temperatures within the range of fromabout 325 C. to about 1000 C. Optimum yields are obtainable attemperatures within the range from about 400 to 550 C. However, sincethe reaction is exothermic, temperatures in excess of 550 C. should notbe used, unless means are provided to carry off the heat liberated inthe course of the reaction. Due to the exothermic nature of thereaction, the temperature of the gaseous reaction mixture will be higherthan the temperature of the feed-entering the system by as much as 75 C.The temperatures referred to are those of the entering gas feed near thereactor inlet.

The preferred reaction pressure is approximately atmospheric, within therange of from about to about 75 p.s.i.g. Higher pressures up to about300 p.s.i.g. can be used and have the advantage of simplifying theproduct recovery.

Only a brief contact time with the catalyst is required for effectivedehydrogenation. The apparent contact time with the catalyst can varyfrom about 0.5 up to about 50 seconds but higher contact times can beused if desired. At these contact times, comparatively small reactorsand small amounts of catalyst can be used effectively.

In general, any apparatus of the type suitable for carrying outoxidation reactions in the vapor phase may be employed in the executionof these processes. The processes may be conducted either continuouslyor intermittently. The catalyst bed may be a fixed bed employing a largeparticulate or pelleted catalyst or, in the alternative, a socalledfluidized bed of catalyst may be employed.

The reactor may be brought to the reaction temperature before or afterthe introduction of the reaction feed mixture. However, in a large-scaleoperation, it is preferred to carry out the process in a continuousmanner, and in such a system, the recirculation of the unreacted olefinis contemplated.

The catalyst compositions and oxidation process of this invention arefurther illustrated in the following examples wherein the amounts of thevarious ingredients are expressed as parts by weight unless otherwisespecified.

In a typical catalyst preparation grams of antimony metal werecompletely oxidized in 3 60 ml. of concentrated nitric acid. To thiswere added 34.4 grams of EXAMPLE 1 and 172.3 grams of Du Pont Ludox HS(an aqueous dispersion of 30% by weight of SiO The mixture was stirredand 28% ammonium hydroxide was added until the pH was about 8. Theresulting slurry was filtered and washed and the cake was divided intofour equal parts. Nitrates of the promoter elements were then added toeach quarter of the filter cake and after thorough blending, the cakewas dried overnight at 120 C. calcined for 24 hours at 800 F. andheat-treated for an additional 8 hours at 1400 F. The base catalystcomposition in this instance consisted of 70 Weight percent FeSb O and30 Weight percent SiO As described earlier, the promoter compounds wereincorporated in the concentration range of from about 1 to 10% by weightbased on the weight of the base catalyst.

A catalyst promoted with 1.5% bismuth was prepared by dissolving 1.1grams of Bi(N0 -5H O in water and the solution was added to a quarter ofthe wet filter cake described above. The resulting promoted catalyst wasdried at 120 C., calcined at 800 F. for 24 hours and heattreated for 8hours at 1400 F. Dry weight of the catalyst was 44 grams.

Similarly, a promoted catalyst was prepared adding an aqueous solutionof .1.9 grams of Cu(NO =3H O to the filter cake. The dry weight of thecatalyst was 41 grams and the active catalyst component contained 1.7%by weight of Cu.

0.6 gram of SnO was added to a portion of the wet filter cake. Thecatalyst was dried at 120 C., calcined at 800 F. for 24 hours andheat-treated for 8 hours at 1400 F. The dry weight of the promotedcatalyst was 47 grams and the active component contained 1.6% by weightof Sn.

1.4 grams of GeCl were treated with concentrated NH OH, and then theresulting material was filtered, washed, and mixed with a portion of wetcatalyst filter cake. The catalyst was dried at 120 C., calcined at 800F. for 24 hours and heat-treated at 1400 F. for 8 hours. Dry weight ofthe catalyst was 41 grams and the active component contained 1.65% byweight of Ge.

EXAMPLE II In a typical preparation of an attrition resistant basecatalyst, 270 grams of antimony metal were completely oxidized in 1000mls. of concentrated HNO 102.7 grams of Fe(NO -9H O were added and themixture was evaporated almost to dryness. 301 grams of Du Pont Ludox (anaqueous sol of 30% by weight SIO2) were added and the mixture wasbrought to a pH of about 8 by the addition of ammonium hydroxide. Thecatalyst was filtered and washed with 600 mls. of water in two portions.The catalyst was then dried at 120 C., calcined at 800 F. for 24 hoursand heat-treated at 1400 F. for 8 hours.

The above catalyst was then mixed with grams of Ludox and extruded. Theextrudate was dried at C. and heat-treated at 1400 F. for 72 hours.

grams of the foregoing catalyst in the size range which would passthrough a 34-mesh screen and be retained on an 80-mesh screen were mixedwith a solution of 0.36 gram of (NH4)6M07024'4H20. The resultingpromoted catalyst was dried at 120 C., calcined at 800 F. for 2 hoursand heat-treated at 1400 F. for 2 hours. This catalyst contained 1.04%by weight of Mo.

EXAMPLE III The promoted catalysts which were prepared according to theprocedures given in Examples I and II were treated in the ammoxidationreaction of propylene with air and ammonia to produce acrylonitrile. Thereactions were carried out in a steady state stainless steelmicro-reactor unit under constant conditions. The reactor contained 5mls. of catalyst (-80-mesh), the contact time was 3 seconds, thereaction temperature was 880 F. and the feed was composed of propylene,ammonia and air in the mole ratios 1:1:12, respectively. The resultsreported in Table I are based on six minute pre-runs followed by a12-minute product collection run. The products were isolated by gaschromatography.

TABLE I Catalyst, percent promoted: Percent 1 1.73% Re 70.0 1.60% Nb65.0 1.73% "Cu 65.0 1.72% Ag 62.5 1.54% Bi 61.8 1.60% Sn 58.9 6.74% Sn68.9 1.51% Te 58.0 1.54% W 58.0 1.65% Ge 57.9 Unpromoted (Control) 50.0

Per pass conversion of propylene to acrylonitrile.

EXAMPLE IV The procedures of Example III were followed in the conversionof propylene to acrolein. The same catalyst charge, contact time andreaction temperature were used. The feed of propylene and air was usedin the mole ratio of 1:10, respectively. The results are given in TableII.

TABLE II Catalyst, percent promoted: Percent 1 1.73% Re 47.9 7.16% Nb37.5 1.73% Cu 50.6 1.72% Ag 55.0 1.60% Sn 39.5 1.51% To 53.0 7.60% Te61.5 1.54% W 38.6 1.53% Pb 43.8 1.59% Pd 40.4 1.54% Cd 37.8 1.51% Zr54.0 Unpromoted 28.2 1.62% Mo 36.4 1.79% Zn 40.3 1.78% Ba 34.8 1.60% Tl46.6 1.24% Ca 35.4 6.60% Ga 46.6 14.50% Ta 42.1 1.48% As 37.

Per pass conversion of propylene to acrylonitrile.

EXAMPLE V The procedure of Example III was followed in the reaction ofisobutylene, ammonia and air to produce methacrylonitrile. Theconditions used in Example III were the same in the present exampleexcept the reaction temperature was 770 F., the contact time was 3.6seconds,

8 the pre-run was 10 minutes, the run was 15 minutes, and the feed moleratio of isobutylene:ammonia:air was 1:1:15, respectively. The resultsare given in Table III.

EXAMPLE VI The procedures of Example V were repeated in the conversionof isobutylene to methacrolein. The molar feed ratio of isobutylene toair was 1: 10, respectively. The results are given in Table IV.

TABLE IV Weight Percent percent per pass of proconversion meter ofisoelement butylenc in to methcatalyst acroleln EXAMPLE VII In a mannersimilar to that given in the preceding examples, a mixture of butene-2and air was converted to butadiene-1,3 in a much more efiicient mannerwith the promoted catalyst than with the unpromoted catalyst.

We claim:

1. A catalyst composition consisting essentially of (A) a base catalystconsisting essentially of the oxides of antimony and iron, the SbzFeatomic ratio being within the range of about 1:50 to 99:1; (B) a carrierconsisting essentially of silica; and (C) a promoter componentconsisting essentially of an oxide of at least one element selected fromthe group consisting of bismuth, copper, tin, germanium, rhenium,niobium, silver, tellurium, tungsten, gallium, lead, tantalum,palladium, cadmium, zirconium, vanadium, nickel, titanium, molybdenum,zinc, barium, calcium, thallium, arsenic and rhodium. said (B) beingpresent in amounts from 5% to by weight based on the combined weights of(A) +(B) and said (C) being present in amounts from about 0.01 to 20% byweight based on the combined weight of 2. The promoted catalystcomposition in accordance with claim 1 wherein the Sb:Fe atomic ratio iswithin the range of about 1:1 to about 25:1 and the promoter componentis present in elementary form in from 0.01 to about 20% by weight basedon the weight of the promoted catalyst composition.

3. The promoted catalyst composition in accordance with claim 2,activated by heating at a temperature above 500 F., but below atemperature deleterious to the catalyst.

4. The promoted catalyst composition of claim 3 wherein the basecatalyst corresponds to the empirical formula Sb I-"e O wherein a is anumber within the range of from about 1 to 99, b is a number within therange of from about 50 to 1 and c is a number taken to satisfy theaverage valences of antimony and iron in the oxidation states in whichthey exist in the catalyst.

References Cited UNITED STATES PATENTS Jennings et a1 25245 6X Callahanet a1. 252-456 Callahan et al. 252456 Callahan et al. 252-464X DANIEL E.WYMAN, Primary Examiner C. F. DEES, Assistant Examiner U.S. Cl. X.R.

